An oxide semiconductor has attracted attention as a semiconductor material applicable to the transistor. For example, Patent Document 1 discloses a semiconductor device achieving high field-effect mobility (simply referred to as mobility or μFE in some cases) with such a structure that a plurality of oxide semiconductor layers are stacked, the oxide semiconductor layers functioning as a channel in the plurality of oxide semiconductor layers contains indium and gallium, and the proportion of indium is higher than the proportion of gallium.
Non-Patent Document 1 discloses that an oxide semiconductor containing indium, gallium, and zinc has a homologous series represented by In1−xGa1+xO3(ZnO)m (x is a number which satisfies −1≤x≤1, and in is a natural number). Furthermore, Non-Patent Document 1 discloses a solid solution range of a homologous series. For example, in the case of a solid solution range of a homologous series when in is 1, x is within a range from −0.33 to 0.08, and in the case of a solid solution range of a homologous series when in is 2, x is within a range from −0.68 to 0.32.